"Olga," I said to my neighbor with tears in my eyes, "I have breast cancer."

"So, who doesn't?" she reponded with a gentle wink.

Olga's comment made my day, reminding me what good company I kept. It momentarily cut through the envy I felt for anyone who appeared healthier than I did, which is to say, everyone.

Unlike most cancer patients, I was used to talking and thinking about cancer. During my training as a psycho-oncologist (a clinical psychologist who specializes in helping people with cancer), I used to be one of the envied, bounding around the hospital in my starchy white coat. It was even worse for one of the psychiatry residents: One of her patients complained that she simply couldn't cope with seeing the resident's beautiful face and thick blond hair every day (both of which I had noted as well).

Now, here I was, envying not only the pretty women but everyone else, too, especially once chemotherapy began. As the flood of hairs fell from my head, I noticed other women's flowing locks like never before. It is one of life's great ironies that we share our mortality with everyone, and yet when we deal with it in our own lives, it's the loneliest feeling there is.

The envy even crept into my relationships with other breast cancer patients, wonderful women, usually friends of friends, who spent hours on the phone with me even though we didn't know each other and we never met in person. I had Stage II invasive lobular carcinoma, and to deal with it I subjected myself to a bilateral mastectomy, reconstruction, chemotherapy and hormone therapy that would likely put me in early menopause. If my new breast cancer acquaintance turned out to have "only" Stage I disease or to need "only" a lumpectomy or no chemo, the inevitable competitiveness set in. How could she know what I was going through when her odds were so much better than mine?

On the other hand, if she turned out to have Stage IIIC, as one new friend did, I felt humbled and guilty. What right did I have to cry, when I still had early-stage cancer and my odds for cure were higher?

There were moments when my envy even gave me strength: Perhaps, I thought, the poison made me tougher than thou. But more often, what made me feel strong was the way the people around me supported me, helping any way they could, babysitting, offering food, errands, love. I don't think cancer is a gift (and, if it is, I'd prefer to be directed to the returns counter). But it taught me to appreciate the very people whose health I begrudged.

I even had to admit that my envy was usually based on a fallacy. How did I know if my friends and neighbors really were healthy themselves? How did I know what their future held, any better than I knew my own? When I was training, a beloved breast surgeon was killed in a car accident in her early 50s. How many of her grieving patients ever expected to outlive her?

Close to the end of my chemo treatment, a woman on an online breast cancer discussion board started a thread. "We complain so much here about what's terrible. How about some examples of positive things that have happened because of your cancer?" she asked.

The posts piled in. One woman wrote of her husband and adult sons taking care of her the way she'd once cared for them. Another wrote of her church group, which instructed her to leave two bins in her driveway; every day during her year-long treatment, the group filled one bin with hot food at dinnertime, the other with cold, making sure she never had to cook for herself. Someone made sure to check in on her every day so she wouldn't feel alone.

I thought of my own positives. A few had to do with my writing and my deepening professional insights, as I now learned my field from the inside out. But mostly, they were testaments to the people in my life, starting with my husband and sons, parents, mother-in-law and everyone else. The people whose health I envied, like my friend Marie, who drove four hours from Maryland just to give me silly gifts and take my boys to the zoo, so I could relax. Or Beth, who drove me three hours and back so that my family and I could go on vacation without my having to miss my weekly treatments in the city.

My envy didn't disappear. But it paled in comparison to these moments.

One woman's response to the thread will stay with me always. Her hair was falling off at lightning speed two weeks into chemo. Distraught, she warned her co-workers that she would shave her head that night and didn't know how she'd look the next day. When she came into work in the morning, she discovered that her male colleagues had shaved their own heads, in solidarity.

Mindy Greenstein is the author of "The House on Crash Corner (and Other Unavoidable Calamities)." She lives in New York with her husband and two sons.